A cellular network is a radio-based network made up of a number of cells. Each cell exists in a geographical area covered/served by one or more transceivers, positioned in a base station. The cells together cover different areas to provide radio coverage over a wider area than that of one cell. The cellular network comprises a number of fixed main transceivers (on base stations) and a number of distributed mobile transceivers which provides services to the users of the network.
A primary issue for a cellular network is the method used for signal distribution between transceivers. One common method is Time Division Multiple Access (TDMA), used in the GSM standard combined with Frequency Division Multiple Access (FDMA). FDMA limits the reuse of a particular frequency due to interference. This means that there must be at least one cell's gap between cells using the same frequency. Another method is Code Division Multiple Access (CDMA) used for instance in 3G standards. CDMA uses a wider frequency band to achieve the same transmission capacity. On the other hand, the frequency band can be used in all cells without any risk of interference. Multiple accesses means that a number of mobile transceivers can share the same communication channel (frequency). In GSM, TDMA allows up to eight time slots per frequency. Since each mobile operator has one unique radio frequency band, these signal methods are essential for using the frequency band as much as possible. Sometimes, the different methods are combined to give multiple channels (transceiver-to-transceiver communication) within the coverage of one cell.
The base station contains the transceivers, antennas and equipment for encrypting/decrypting communication with the base station controller (BSC) serving several base stations. In a UMTS (W-CDMA) the base station controller is known as the Radio Network Controller (RNC). Typically, the base station contains several transceivers to be able to serve several different frequencies within the band. The base stations serve/cover the different cells (geographical areas) of the cellular network and together build the complete network for a supplier. By using directional antennas on a single base station, each pointing in different directions, it is possible to sectorice the base station so that several different cells are served from the same location, using the same frequencies. This increases the traffic capacity of the base station whilst not greatly increasing the interference caused to neighboring cells.
The base/radio station controller controls and supervises a network or a network segment, a segment being a part of a network. The controller communicates with a large number of transceivers (either directly or through a communication device for a group of transceivers) and handles allocation of radio channels, receive data from mobile phones, control handovers (communication session passing from one cell to another) and being a link between the transceivers and the Mobile Switching Center (MSC). It sometimes even works as a full switching station handling the traffic. Through the MSC the voice traffic from the mobile phone is routed (after checking with the phone operator register if it is allowed) to the Public Switched Telephone Network (PSTN) using SS7 (a set of telephony signaling protocols). SS7 delivers cell mobile telephone call across the PSTN.
The base/radio station controller is a key element is a cellular network. It controls the network segment and controls handover and roaming. It also works as a node for the MSC. The controller is aware of the cells in neighboring networks and network segments to which it can hand over communication sessions. The controller keeps a record (list) of the external cells and keeps a geographical map (mapping) of which cells is its own cellular network that have relationship to those external cells. The relationship is held in the form of an object-oriented model. The 3GPP association specifies the standards for the different kind of network, such as GSM and UMTS (W-CDMA). In the 3GPP Technical Specifications 32.642 (V6.6.0) and 32.652 (V6.2.1) it is shown how the mapping is maintained by the base/radio station controllers so that they can keep track of external cells and the relationship of those cells to the controller's local cells within its own network. A local cell can have relationship with an external cell in its own kind of network or with an external cell in a different kind of network. Creating such a record (list) for a cell is complex and different algorithms are used together with input data from field measurements or computer predictions of radio wave propagation in the areas covered by the cells.
Information about the relationship between local cells (controlled by the same controller) and external cells (controlled by a different controller) is used in case of handover, which is the process for transferring ongoing communication sessions from one cell to another. One kind of handover is hard handover (in TDMA/FDMA) in which the session is transferred when the channel of the source cell releases it and then the channel of the target cell engages it. Another kind is soft handover (in CDMA) in which the channel of the source cell is retained and used for a while in parallel with the channel of the target cell. In this case the connection to the target is established before the connection to the source is broken. Reasons for handover is for instance a mobile phone moving for instance from a local cell to an external cell, lack of capacity within one cell, interference in case of FDMA/TDMA or changed moving behavior. A typical handover is when the session is redirected from one segment to another. As described later, each cell in a cellular network is assigned a list of potential target cells for handover
Information about the relationship between local cells (within the same network) and external cells (within a different network) is also used in case of roaming, wherein the subscriber's mobile operator hands over the communication session in its own cellular network to another mobile operator's cellular network (the details of the roaming process will not be dealt with here). The two operators have an agreement that allows roaming and communication and subscription data is exchanged between their respective cellular networks when roaming. In some cases, roaming occurs is the home area of an operator due to a weak signal. Reasons for roaming are the need for a new operator to provide full geographic at start-up, international roaming due to country-based operators or networks of different technology. Roaming between networks of different technologies is a great challenge, and there are many standards in how to achieve interoperability between such networks.
The base station typically comprises a base station control function through which the base station controller controls the station and which also provides an Operations and Maintenance connection to the network management system. A network management system provides a package of end-user functions for the operation of the cellular network. The functions refer to operation and maintenance of the network at a higher level. Examples of such functions are:                1. Hardware management—continuously keep inventory of all hardware present.        2. Software management—installation, upgrade, configuration activities etc.        3. Configuration management—enables the operator to set, modify and examine configuration parameters and files.        4. Performance management—provides data on the network performance with respect to accessibility, retainability etc.        5. Fault management—handling, subscription and logging of alarms and event.        
Network management software may in some cases be installed in any node in the network and provides a GUI (graphical user interface) for operation. The management system supports the day-to-day operation and maintenance procedures. The network management traffic is normally separated from user/signalling traffic, but is carried on the same physical links. The traffic can be thought of as logical or virtual links. Interfaces are used for providing the management communication with the network.
The management system 11 of a cellular network 10 (in large networks more than one system may be used) handles the configuration of external cells and the mentioned record (list) of the relationship with local cells in a particular base/radio station controller 12, see FIG. 1. Periodically, the system updates the external cell configuration in the controllers by the steps of:                1. Reading details of the local cells, external cells and their relationship from each controller        2. Reading details of the external cells and their relationship from each controller.        3. Using the data read to determine the optimum definition for external cells and their relationships from each controller.        4. Changing the configuration on each controller so that the external cell definition on that controller is optimal.        
Where the cellular network has more than one management system 10, the systems either exchange information 13 about its respective controllers or passes it to a single master management system 14, see FIG. 2, which sets the configuration of all controllers.
There are some drawbacks with the existing record method for handover and roaming. In said drawbacks the external cell is a cell within a different network segment or within a different network:                1. The external cell and its relationships are set by the management system/-s and not by the network itself. This means that the configuration of respective cell and its relationships is managed external to the network manually by the management system. In case of more than one system, the management systems exchange information and cooperate to enable this or pass it to a master management system. If there is an inconsistency between the data in two or more management systems, these have to be resolved manually.        2. The external cell and its relations with local cells cannot adapt to changes in the network conditions, which means that it is not possible for the external cell and its relations to be defined and removed in an ad-hoc manner as new cells appear and disappear in the external networks or network segments or as load condition change in the networks.        3. The management systems runs its configuration task periodically, which means that the configuration for external and local cells and their relationships is only up to date at the time the last configuration was executed.        4. The network management system must be aware of external cells in all other networks which are adjacent to or overlapping the local cells they are managing. This means that management systems must exchange information and co-operate. As new networks (new operator and/or technology) the number and type of networks a management system must interact with increases dramatically.        5. The management system must be aware of all of the cell data in the network or networks they are configuring in order to calculate all the cell and relationship data. They must also be aware of the details of which network technologies can interact and how they interact.        
As disclosed these are problems typical for a hierarchical management structure. There is only one single network management hierarchic topology in the network, which is static and represents the connectivity for the management systems of the network. The management systems have to interact fully and as said the difficulties in interaction increases with the number and kind of networks introduced. The systems are fully dependent on each other and the information they can share. A bad working interaction between two management systems will weaken the whole structure. Also, as said, the update of the relationships is static due to the structure and the periodicity of the configuration. One effect is that the development of management systems focuses more on the ability to monitor the cells of the networks than how to manage and provide better features for management.